I’m sitting on a concrete slab in Tinqui, Peru, a strangely ghost-townish village in the Andes. This is a place where otherwise sane people start and end a massive 55-mile hike around a skyscraping mountain called Ausangate. And as I squint through the morning sunlight at the horseman loading my red pack onto a pony it occurs tome that I am one of these people. Against my better judgment, I have signed on—along with eight other women and two men—to do this climb. Three sinewy French trekkers who have just returned from the peak stand next tome peeling off layers of Polartec fleece. They smell like acrid sweat and describe their experience only as “very cold at night.” All I’ve done today is step off a bus, and already I’m exhausted. I am not an athlete.

This, in fact, was my mother’s stock answer when strangers inevitably asked if her gangly-limbed, five-foot-eight daughter played basketball. She’d feign exasperation, throwing her arms up for effect, but I always sensed her relief. Thanks to my congenital klutziness and fear of flying round objects, she and my father, with their graduate degrees and New York Times—smudged fingers, would never have to spend an evening in the high school gym bleachers, enduring bad acoustics and the tedium of watching me dribble an orange ball up and down the court.

I came of age during the mid-eighties, a decade and a half after the 1972 passage of Title IX, which essentially brought competitive high school and college sports for girls into the mainstream. But at 13, I was wholly uninterested in chasing a ball. I was, however, fascinated by the girls who did. During what was for me the single most awkward year of a pretty awkward life, they blossomed into warriors with powerful bodies and lips that curled ruthlessly into fierce shapes when they cracked their bats across softballs. They had sleek ponytails that bounced when they walked. In high school they grew into the jockettes, an amorphous clique of girls in Reeboks and oversize sports jerseys. Meanwhile my crowd passed the time at thrift stores or in dimly lit rooms listening to the Sex Pistols. We didn’t do softball. Or field hockey or lacrosse. My aversion to all things sports related became etched into the loops and whorls of my social fingerprint.

True, I’d turned into the kind of adult who dutifully drags her ass to the gym and slogs through the same 25-minute jog three times a week. I write fitness stories for a living, and I know how many calories are burned every minute on the treadmill. But with each Nike billboard I pass on the highway, every blurb I read about the growing legions of women surfers, every once-mortal friend who is suddenly hauling off to triathlon practice (triathlon practice!) five nights a week after work, I’m reminded that I’ve never once tested my body’s limits. Never once fractured a bone or bruised my shins or crossed a finish line. And if you reach your 30s without doing any of that, your chances of ever doing it are pretty slim.

So when Miriam Nelson, PhD, the director of the John Hancock Center for Physical Activity and Nutrition at Tufts University invited me to cover a trek she was leading through Peru’s rugged Cordillera Vilcanota mountain range, my first thought was, lam not that kind of girl. I’m not a marathon runner or a world-class ice climber, like two other women on the tip. I’ve never felt a burning desire to sleep—and pee—close to nature. Or climb mountain passes at almost 17,000 feet. Or breathe air so thin that I’d have men with horses and tanks of oxygen at my disposal, just in case.

Nelson, a lean, blonde bolt of muscle who calls herself Mim, would probably do this stuff every day if she could. When she isn’t giving college lectures or appearing on PBS specials, she’s skiing in Chamonix, France, or running up steep hills for fun. Together with Lluminari, a brain trust of the kinds of charismatic health experts you see on Good Morning America, she produces weekend wellness retreats and more formidable small-group excursions to, among other places, this remote mountain in South America where she’s convinced my inner jock is hiding. The fact that I actually came to believe this proves how persuasively Mim preaches the gospel of athleticism. I can’t say why, exactly, I suddenly felt the burning need to climb so high that I might require supplemental oxygen—and keep climbing for six days. Possibly for the same reason Mim’s so-something sister-in-law Liz, signed up despite her crippling arthritis. Or because of what drew in Lilian and Carola, both in their 50s, both breast cancer survivors.

And frankly the notion that my body might crap out halfway up the mountain—that I might succumb to altitude sickness or fall off some rocky precipice — didn’t seem to cross Mim’s mind. And pretty soon, it stopped crossing mine. I’d been vaccinated against hepatitis A, yellow fever, and tetanus. I’d tapped my local camping store for deep pink Duofold hiking tops, North Face fleece, “smart wool” socks, and khaki everything. (Why are outdoor enthusiasts so okay with this noncolor?) I’d rented a subzero sleeping bag. Then I’d stuffed it all into my pack, along with some energy bars, a roll of toilet paper, and a small bottle of Purell, and left for the other end of the earth.

The hike is under way Tinqui vanishes behind us and Ausangate’s snowy peaks emerge against a canvas of blue sky When the late-day sunlight finally gives way to bracing winds—it’s July, which is winter in Peru—I remember that my down jacket is packed away on one of our horses, alongside the thin tent I’ll be sleeping in tonight. In what will become a nightly ritual, we all wriggle into every goose down item available and huddle around a table, eating quickly and desperately our bodies reeling from the day’s climb, our brains anticipating what’s coming next. “You burn 3,000 to 4,000 calories a day in the mountains,” Mim tells us.

By noon the next day, I believe it, as we plod toward a 15,580-foot pass, its moonlike landscape of coffee-colored earth dotted with the odd tuft of pale, prickly moss. Occasionally we see Peruvian women, squinting at us through lined skin. I wonder what they think of us, with our hiking poles, sunglasses, and maps showing that, after climbing and descending for miles and miles, we’ll wind up back where we started.

They’d think we were nuts. Especially if they knew l could hop onto a horse anytime—but I won’t.

As the days pass, I eventually watch others assume the saddle, yet somehow, despite my altitude-induced migraines and roiling nausea, I refuse to do the same. If anything, my symptoms harden my determination to push on, to return home with calluses, rock-hard calves, and war stories of being the first, the fastest, the strongest. Because what’s the sense in traveling to a mountain on the other end of the earth to go for a trail ride?

By the time we approach the last pass of the trek, I’ve fallen to the back of the line. At this point, I’m too busy trolling for oxygen molecules—which are few and far between up here— to care. When we reach the top, there’s much hugging and a frantic snapping of digital cameras, as if a one- gigabyte chip has the power to preserve the fleeting moment when ten mortal bodies become divine. Beneath my fleece and down and silk long underwear, I feel my heart pounding against my rib cage, my muscles straining against my skin. Back at our campsite on that final night, I write this in my journal: “This instinct to crawl outside our comfort zones and do things that seem beyond our ability just to prove that we can—is it a human drive?”

I’d say so—it’s a drive to feel that humanness in every cell of our hearts and bones. ‘What else accounts for marathon runners, astronauts, and Venus Williams? These people, I suppose, have always known that the body is an exquisitely designed machine created for higher things than riding in cars, slumping in office chairs, and running in place. The jockettes knew it, too. It wasn’t until I stood on top of the world and crossed a finish line that I figured it out. They say people experience life-changing epiphanies in sacred, windswept places. Here is mine—and I think I’ve shown I’m an unlikely person to make it: We are all athletes. Anyone who has breath in her lungs and muscles stretched over her bones longs—sometimes consciously, sometimes not—to find out what her body is truly capable of. And once that happens, there’s no telling what heights her gangly legs will scale.